The connecting rod of internal combustion engines typically consist of a connecting-rod shank and two end bearings, which link the piston and the corresponding crank pin of a crankshaft to a powertrain. One end performs oscillating motions, the other moves with the crank pin in the crank circle, so that a so-called “violin-shaped connecting rod,” i.e., a violin-shaped motion curve of the connecting rod, is created.
From DE 35 05 964 C1, a powertrain with a connecting rod is known, which comprises, in a typical way, an end bearing in the form of a connecting-rod head, i.e., the upper connecting-rod eye, a connecting-rod shank, and an opposite end bearing in the form of the connecting-rod bearing, i.e., the lower connecting-rod eye. Such an arrangement represents a connecting-rod element between the straight part of a crank drive, thus to the piston, and the crankshaft. The connecting-rod head can be complete or in parts. The bearing cover of the divided connecting-rod bearing, thus of the lower connecting-rod eye, is connected to the connecting-rod foot by at least two fitted strain screws. The connecting-rod bearing is formed by the connecting-rod foot and connecting-rod cover, in which bearing shells expand into a complete bearing sleeve. In addition, such connecting-rod bearing receives the crank pin and associated impact-like stresses when the pressure changes, which produce high bearing loads. Because the connecting rod must be guided partially through the engine cylinder when the piston is assembled, at least for a strong crank pin the lower connecting-rod eye or the connecting-rod shank generally had to be divided.
The piston operates under great mechanical and thermal loads. At the same time it must perform several tasks, such as the conversion of pressure energy into mechanical work, sealing of the cylinder chamber from the crankcase, and straight guidance of the upper end of the connecting rod in so-called trunk piston engines. The bearing of the piston on the connecting-rod head has included a piston bolt in the connecting-rod eye, which transferred the forces evenly between piston and connecting rod. Previously, the position of the piston bolt had been determined by two factors. To prevent tipping motions of the piston, its center of gravity should lie on the axis of the bolt. On the other hand, the piston bolt must be fixed in the center of the shaft of the piston so that the normal force is transferred uniformly to the cylinder wall. Because both demands cannot be satisfied simultaneously, the piston bolt previously had been installed slightly above the center of the shaft.
Large pistons of a known type have been made of two or more parts. Thus, the piston base, e.g., made from steel or case iron, is screwed together with the shaft, e.g., made from special cast iron or an aluminum alloy.
From DE 100 46 214 C1, a powertrain is further known, for which a connecting rod is used in the form of a marine head with a one-part connecting-rod shank (which means savings in terms of weight and cost, compared with a connecting-rod shank divided for assembly reasons), which features a special configuration of connecting-rod bearing for receiving the crank pin, and thus enables a compact construction. For this reason, a smaller overall engine height also is possible and the drawing of the piston through the engine cylinder is eased considerably.
Now there is also the need to optimize the bearing of the piston on the connecting-rod head, which had been effected previously by means of a piston bolt, which transfers the forces between the piston and the connecting rod and the connecting-rod eye. In particular, there is the need to form this piston/connecting-rod connection more compactly and to make the piston assembly even simpler.